The present invention is related to a technique for transferring data from a certain storage apparatus to the storage apparatus 102 installed at a remote site.
Disaster recovery technical ideas have been prepared for such a case that failures happen to occur in a storage apparatus connected to a host apparatus due to disaster and the like in such a way that while another storage apparatus is installed at a remote place, data are saved to this storage apparatus installed at the remote place. In this case, the storage apparatus connected to the host apparatus will be referred to as a “main storage apparatus”, whereas the storage apparatus arranged at the remote place with respect to the “main storage apparatus” will be referred to as a “sub-storage apparatus” hereinafter. Technical ideas have been proposed in a system equipped with a main storage apparatus and a sub-storage apparatus, by which data is transferred from the main storage apparatus to the sub-storage apparatus in either a synchronous manner or an asynchronous manner (refer to, for example, JPA-2005-222110).
In the case that the data is transmitted from the main storage apparatus to the sub-storage apparatus in the synchronous manner, the data writing operations with respect to both the main storage apparatus and the sub-storage apparatus are accomplished in response to a write request issued from the host apparatus, and thereafter, a response is returned to the host apparatus. On the other hand, in the case that the data is transmitted from the main storage apparatus to the sub-storage apparatus in the asynchronous manner, before the data is written into the sub-storage apparatus, a response is returned to the host apparatus. Thereafter the data is transmitted from the main storage apparatus to the sub-storage apparatus so as to be written into the sub-storage apparatus.